Congratulation to Claudia Lunghi who has won the prize for the best thesis in biomedical research in Florence University for 2013! The competition was very tought as it concerned all biomedical departments in Florence University, nevertheless Claudia obtained an outstanding victory with her study on binocular rivarly and brain plasticity. Well done Claudia, you are a champion!

Resolution of perceptual ambiguity is one function of cross-modal interactions. Here we investigate whether auditory and tactile stimuli can influence binocular rivalry generated by interocular temporal conflict in human subjects. Using dichoptic visual stimuli modulating at different temporal frequencies, we added modulating sounds or vibrations congruent with one or the other visual temporal frequency. Auditory and tactile stimulation both interacted with binocular rivalry by promoting dominance of the congruent visual stimulus. This effect depended on the cross-modal modulation strength and was absent when modulation depth declined to 33%. However, when auditory and tactile stimuli that were too weak on their own to bias binocular rivalry were combined, their influence over vision was very strong, suggesting the auditory and tactile temporal signals combined to influence vision. Similarly, interleaving discrete pulses of auditory and tactile stimuli also promoted dominance of the visual stimulus congruent with the supra-modal frequency. When auditory and tactile stimuli were presented at maximum strength, but in anti-phase, they had no influence over vision for low temporal frequencies – a null effect again suggesting audio-tactile combination. We also found that the cross-modal interaction was frequency-sensitive at low temporal frequencies, when information about temporal phase alignment can be perceptually tracked. These results show that auditory and tactile temporal processing is functionally linked, suggesting a common neural substrate for the two sensory modalities, and that at low temporal frequencies visual activity can be synchronized by a congruent cross-modal signal in a frequency-selective way, suggesting the existence of a supra-modal temporal binding mechanism.

In natural scenes, objects rarely occur in isolation but appear within a spatiotemporal context. Here, we show that the perceived size of a stimulus is significantly affected by the context of the scene: brief previous presentation of larger or smaller adapting stimuli at the same region of space changes the perceived size of a test stimulus, with larger adapting stimuli causing the test to appear smaller than veridical and vice versa. In a human fMRI study, we measured the blood oxygen level-dependent activation (BOLD) responses of the primary visual cortex (V1) to the contours of large-diameter stimuli and found that activation closely matched the perceptual rather than the retinal stimulus size: the activated area of V1 increased or decreased, depending on the size of the preceding stimulus. A model based on local inhibitory V1 mechanisms simulated the inward or outward shifts of the stimulus contours and hence the perceptual effects. Our findings suggest that area V1 is actively involved in reshaping our perception to match the short-term statistics of the visual scene.

Despite the existence of much evidence for a number sense in humans, several researchers have questioned whether number is sensed directly or derived indirectly from texture density. Here, we provide clear evidence that numerosity and density judgments are subserved by distinct mechanisms with different psychophysical characteristics. We measured sensitivity for numerosity discrimination over a wide range of numerosities: For low densities (less than 0.25 dots/deg2), thresholds increased directly with numerosity, following Weber’s law; for higher densities, thresholds increased with the square root of texture density, a steady decrease in the Weber fraction. The existence of two different psychophysical systems is inconsistent with a model in which number is derived indirectly from noisy estimates of density and area; rather, it points to the existence of separate mechanisms for estimating density and number. These results provide strong confirmation for the existence of neural mechanisms that sense number directly, rather than indirectly from texture density.

BREAKING NEWS:

From Europe an Advanced Grant for Professor Maria Concetta Morrone

The ERC grants funding of 2.5 million euros to a Pisa University professor for a study project in the field of cognitive neuroscience

A project from Pisa University has been awarded an Advanced Grant from the European Research Council (ERC): Maria Concetta Morrone, Professor of Physiology at the university, has been granted funding of 2.5 million euros for the period 2014-2018 with a research project in the field of cognitive neuroscience. "Early cortical sensory plasticity and adaptability in human adults" is the title of the project, which aims to investigate the plasticity and the capacity for change of the adult brain through experimental studies carried out in a clinical environment and which concentrate in particular on visual properties.

The study will be carried out with the scientific collaboration of the Institute of Neuroscience of the CNR and will also involve the Stella Maris Foundation and their Imago 7 scanner. "Neuronal plasticity is an important mechanism for memory and cognition," explains Professor Morrone. "It has long been thought that sensory neural systems are plastic only during the so-called 'critical period', that is to say only capable of changing structure and function at an early age. With this project we will demonstrate that this capacity for change is also present in the adult brain and particularly for basic visual properties like ocular dominance."The research team led by Maria Concetta Morrone, which also includes researchers from the Institute of Neuroscience of the CNR, Florence University, the Stella Maris Foundation, the Meyer Children's Hospital and Oxford University, has already investigated the high degree of plasticity in the adult visual cortex, paving the way for new and important applications in diagnostic and therapeutic fields and in particular in the treatment of children with amblyopia (or 'lazy eye').

In the course of the project funded by the ERC, the researchers will propose a series of experiments organized within different lines of research, the first of which will study the effects of brief periods of monocular deprivation on the reorganization of the visual cortex in adults, while another will analyze the clinical implications of monocular patching of children with amblyopia and the functional exploration of the visual cortex in newborns.

The research team is made up of numerous researchers from Tuscany who have worked with Maria Concetta Morrone for quite some time, such as Professor Giovanni Cioni, Dr. Michela Tosetti from the Stella Maris Foundation, Professor David Burr from Florence University (one of the first ERC grantees in Italy) and several young doctoral candidates and postdocs.

Research

New Research in Journal Of Neuroscience

Congratulations to Concetta, whose latest paper has just been accepted for publication in JN.

Visually responsive neurons typically exhibit a monotonic-saturating increase of firing with luminance contrast of the stimulus, and are able to adapt to the current spatiotemporal context by shifting their selectivity, being therefore perfectly suited for optimal contrast encoding and discrimination. Here we report the first evidence of the existence of neurons showing selective tuning for contrast in area V4d of the behaving macaque (Macaca mulatta), i.e. narrow band-pass filter neurons with peak activity encompassing the whole range of visible contrasts and pronounced attenuation at contrasts higher than the peak. Crucially, we found that contrast tuning emerges after a considerable delay from stimulus onset, likely reflecting the contribution of inhibitory mechanisms. Selective tuning for luminance contrast might support multiple functions, including contrast identification and the attentive selection of low contrast stimuli.

Several studies have demonstrated enhanced auditory processing in the blind, suggesting that they compensate their visual impairment in part with greater sensitivity of the other senses. However, several physiological studies show that early visual deprivation can impact negatively on auditory spatial localization. Here we report for the first time severely impaired auditory localization in the congenitally blind: thresholds for spatially bisecting three consecutive, spatially-distributed sound sources were seriously compromised, on average 4.2-fold typical thresholds, and half performing at random. In agreement with previous studies, these subjects showed no deficits on simpler auditory spatial tasks or with auditory temporal bisection, suggesting that the encoding of Euclidean auditory relationships is specifically compromised in the congenitally blind. It points to the importance of visual experience in the construction and calibration of auditory spatial maps, with implications for rehabilitation strategies for the congenitally blind.

During development, within a specific temporal window called the critical period, the mammalian visual cortex is highly plastic and literally shaped by visual experience; to what extent this extraordinary plasticity is retained in the adult brain is still a debated issue. We tested the residual plastic potential of the adult visual cortex for both achromatic and chromatic vision by measuring binocular rivalry in adult humans following 150 minutes of monocular patching. Paradoxically, monocular deprivation resulted in lengthening of the mean phase duration of both luminance-modulated and equiluminant stimuli for the deprived eye and complementary shortening of nondeprived phase durations, suggesting an initial homeostatic compensation for the lack of information following monocular deprivation. When equiluminant gratings were tested, the effect was measurable for at least 180 minutes after reexposure to binocular vision, compared with 90 minutes for achromatic gratings. Our results suggest that chromatic vision shows a high degree of plasticity, retaining the effect for a duration (180 minutes) longer than that of the deprivation period (150 minutes) and twice as long as that found with achromatic gratings. The results are in line with evidence showing a higher vulnerability of the P-pathway to the effects of visual deprivation during development and a slower development of chromatic vision in humans.